We have defined a new approach to the use of monoclonal antibodies for diagnosis and therapy of tumor in lymph nodes: delivery to the nodes via lymphatic vessels after subcutaneous injection. To establish a firm pharmacokinetic basis for this approach, we first studied to normal cell types in the mouse lymph node. In vitro binding characteristics were combined with in vivo pharmacological parameters to develop a quantitative understanding of the delivery process using the SAAM computer modeling system. Armed with that background information, we then demonstrated and analyzed specific uptake in lymph node metastases of a guinea pig tumor. Imaging studies were followed up with attempts at therapy. For diagnosis of early metastatic tumor in the nodes, the lymphatic route can be expected to provide higher sensitivity, lower background, lower systemic toxicity, and faster localization than the intravenous route. It will also minimize the problem of cross-reactivity with antigen present on normal tissues. The experimental design of the guinea pig studies is currently being applied to detection of lymph node metastases in clinical stage II malignant melanoma, breast cancer, and cutaneous T-cell lymphoma (CTCL). A similar protocol has been approved for non-small cell lung cancer. Our studies of CTCL have produced the most efficient imaging of tumor cells yet achieved in humans by any techniques. In vitro and animal studies are being continued both to optimize the clinical procedures and to explore basic functions of the immune system. Our longer term aim is to understand the pharmacology of monoclonal antibodies and other ligands in order to develop criteria for rational molecular design of biological antitumor agents.